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	<div id="pagetitle"><h1>YUI Library Examples: JSON Utility: Rebuilding class instances from JSON data</h1></div>
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	<h1>JSON Utility: Rebuilding class instances from JSON data</h1>
	
	<div class="exampleIntro">
	<p>This example illustrates one method of serializing and recreating class instances by using the <code>replacer</code> and <code>reviver</code> parameters to <code>JSON.stringify</code> and <code>JSON.parse</code> respectively.</p>
			
	</div>	
					
	<div class="example-container module ">
			<div class="hd exampleHd">
			<p class="newWindowButton yui-skin-sam"><!--<span id="newWindowLinkx"><span class="first-child">--><a href="json_freeze_thaw_clean.html" target="_blank">View example in new window.</a><!--</span></span>-->		
		</div>		<div id="example-canvas" class="bd">
	
		
	<!--BEGIN SOURCE CODE FOR EXAMPLE =============================== -->
	
	<div id="demo">
    <button type="button" id="demo_freeze">Freeze</button>
    <button type="button" id="demo_thaw" disabled="disabled">Thaw</button>
    <textarea id="demo_frozen">(stringify results here)</textarea>
    <div id="demo_thawed"></div>
</div>

<script type="text/javascript">
YAHOO.util.Event.onDOMReady(function () {

var Event = YAHOO.util.Event,
    Dom   = YAHOO.util.Dom,
    JSON  = YAHOO.lang.JSON,
    Demo;
    
Demo = YAHOO.namespace('demo').FreezeThaw = {
    data       : null,
    jsonString : null,

    cryo : function (k,o) {
        return (o instanceof CaveMan) ? CaveMan.freeze(o) : o;
    },
    revive : function (k,v) {
        // Turn anything that looks like a UTC date string into a Date instance
        if (typeof v === 'string') {
            return JSON.stringToDate(v);;
        }
        // Check for cavemen by the _class key
        if (v instanceof Object && v._class == 'CaveMan') {
            return CaveMan.thaw(v);
        }
        // default to returning the value unaltered
        return v;
    }
};

function CaveMan(name,discovered) {
    this.name       = name;
    this.discovered = discovered;
};
CaveMan.prototype.getName = function () {
    return this.name + ", the cave man";
}

// Static methods to convert to and from a basic object structure
CaveMan.thaw = function (o) {
    return new CaveMan(o.n, o.d);
};
// Convert to a basic object structure including a class identifier
CaveMan.freeze = function (cm) {
    return {
        _class : 'CaveMan',
        n : cm.name,
        d : cm.discovered // remains a Date for standard JSON serialization
    };
};

Demo.data    = {
    count : 1,
    type  : 'Hominid',
    specimen : [
        new CaveMan('Ed',new Date(1946,6,6))
    ]
};

Event.on('demo_freeze','click',function (e) {
    Demo.jsonString = JSON.stringify(Demo.data, Demo.cryo);

    Dom.get('demo_frozen').value = Demo.jsonString;
    Dom.get('demo_thaw').disabled = false;
});

Event.on('demo_thaw','click',function (e) {
    var parsedData = JSON.parse(Demo.jsonString, Demo.revive);
        cm = parsedData.specimen[0];

    Dom.get('demo_thawed').innerHTML =
        "<p>Specimen count: " + parsedData.count + "</p>"+
        "<p>Specimen type: " + parsedData.type + "</p>"+
        "<p>Instanceof CaveMan: " + (cm instanceof CaveMan) + "</p>"+
        "<p>Name: " + cm.getName() + "</p>"+
        "<p>Discovered: " + cm.discovered + "</p>";
});

});
</script>
	
	<!--END SOURCE CODE FOR EXAMPLE =============================== -->
	
		
		</div>
		
	
	</div>			
	</div>
		
	<h3>The CaveMan class</h3>
<p>For this example, we'll use a class CaveMan, with a property <code>discovered</code> that holds a <code>Date</code> instance, and a method <code>getName</code>.</p>
<textarea name="code" class="JScript" cols="60" rows="1">
YAHOO.util.Event.onDOMReady(function () {

// set up some shortcuts
var Event = YAHOO.util.Event,
    Dom   = YAHOO.util.Dom,
    JSON  = YAHOO.lang.JSON,
    Demo;

function CaveMan(name,discovered) {
    this.name       = name;
    this.discovered = discovered;
};
CaveMan.prototype.getName = function () {
    return this.name + ", the cave man";
}

...
</textarea>

<h3>Add <code>freeze</code> and <code>thaw</code> static methods</h3>
<p>We'll add the methods responsible for serializing and reconstituting instances to the CaveMan class as static methods.</p>
<textarea name="code" class="JScript" cols="60" rows="1">
// Static method to convert to a basic structure with a class identifier
CaveMan.freeze = function (cm) {
    return {
        _class : 'CaveMan',
        n : cm.name,
        d : cm.discovered // remains a Date for standard JSON serialization
    };
};

// Static method to reconstitute a CaveMan from the basic structure
CaveMan.thaw = function (o) {
    return new CaveMan(o.n, o.d);
};
</textarea>

<h3>Reference the methods in replacer and reviver functions</h3>
<p>We'll create a <code>demo.FreezeThaw</code> namespace to hold our moving parts.  In it, we'll add a method to pass to <code>JSON.stringify</code> that calls our custom serializer, and another method to pass to <code>JSON.parse</code> that detects the serialized structure and calls our thawing method.</p>
<textarea name="code" class="JScript" cols="60" rows="1">
Demo = YAHOO.namespace('demo').FreezeThaw = {

    cryo : function (k,o) {
        return (o instanceof CaveMan) ? CaveMan.freeze(o) : o;
    },

    revive : function (k,v) {
        // Check for cavemen by the _class key
        if (v instanceof Object && v._class == 'CaveMan') {
            return CaveMan.thaw(v);
        }
        // default to returning the value unaltered
        return v;
    }
};
</textarea>

<h3>The data to be serialized</h3>
<p>We'll create a CaveMan instance and nest it in another object structure to illustrate how the thawing process still operates normally for all other data.</p>
<textarea name="code" class="JScript" cols="60" rows="1">
Demo.data = {
    count : 1,
    type  : 'Hominid',
    specimen : [
        new CaveMan('Ed',new Date(1946,6,6))
    ]
};
</textarea>

<h3>Thawing from the inside out and the <code>Date</code> instance</h3>
<p>The reviver function passed to <code>JSON.parse</code> is applied to all key:value pairs in the raw parsed object from the deepest keys to the highest level.  In our case, this means that the <code>name</code> and <code>discovered</code> properties will be passed through the reviver, and <em>then</em> the object containing those keys will be passed through.</p>
<p>We'll take advantage of this and apply <code>YAHOO.lang.JSON.stringToDate</code> to all string values, which will reconstitute Date instances when they match the iso8601 UTC format that JSON serializes Dates to by default.</p>
<textarea name="code" class="JScript" cols="60" rows="1">
Demo = YAHOO.namespace('demo').FreezeThaw = {

    cryo : function (k,o) {
        return (o instanceof CaveMan) ? CaveMan.freeze(o) : o;
    },

    revive : function (k,v) {
        // JSON.stringToDate turns strings in the iso8601 UTC format into Dates
        if (typeof v === 'string') {
            return JSON.stringToDate(v);
        }
        // Check for cavemen by the _class key
        if (v instanceof Object && v._class == 'CaveMan') {
            return CaveMan.thaw(v);
        }
        // default to returning the value unaltered
        return v;
    }
};
</textarea>

<p>Now when the reviver function is evaluating the object it determines to be a CaveMan, the <code>discovered</code> property is correctly containing a <code>Date</code> instance.</p>

<h3>Choose your serialization</h3>
<p>You'll note there are two freeze and thaw operations going on in this example.  One for our CaveMan class and one for <code>Date</code> instances.  Their respective serialization and recreation techniques are different.  You are free to decide the serialized format of your objects.  Choose whatever makes sense for your application.</p>

<h3>Show and Tell</h3>
<p>Now we add the event handlers to the example buttons to call <code>JSON.stringify</code> and <code>parse</code> with our <code>example.cryo</code> and <code>example.revive</code> methods, respectively.</p>
<textarea name="code" class="JScript" cols="60" rows="1">
Event.on('demo_freeze','click',function (e) {
    Demo.jsonString = JSON.stringify(Demo.data, Demo.cryo);

    Dom.get('demo_frozen').value = Demo.jsonString;
    Dom.get('demo_thaw').disabled = false;
});

Event.on('demo_thaw','click',function (e) {
    var x  = JSON.parse(Demo.jsonString, Demo.revive);
        cm = x.specimen[0];

    Dom.get('demo_thawed').innerHTML =
        "<p>Specimen count: " + x.count + "</p>"+
        "<p>Specimen type: " + x.type + "</p>"+
        "<p>Instanceof CaveMan: " + (cm instanceof CaveMan) + "</p>"+
        "<p>Name: " + cm.getName() + "</p>"+
        "<p>Discovered: " + cm.discovered + "</p>");
});

}); // end of onDOMReady handler
</textarea>

<h3>Full Code Listing</h3>
<textarea name="code" class="JScript" cols="60" rows="1">
YAHOO.util.Event.onDOMReady(function () {

var Event = YAHOO.util.Event,
    Dom   = YAHOO.util.Dom,
    JSON  = YAHOO.lang.JSON,
    Demo;
    
Demo = YAHOO.namespace('demo').FreezeThaw = {
    data       : null,
    jsonString : null,

    cryo : function (k,o) {
        return (o instanceof CaveMan) ? CaveMan.freeze(o) : o;
    },
    revive : function (k,v) {
        // Turn anything that looks like a UTC date string into a Date instance
        if (typeof v === 'string') {
            return JSON.stringToDate(v);;
        }
        // Check for cavemen by the _class key
        if (v instanceof Object && v._class == 'CaveMan') {
            return CaveMan.thaw(v);
        }
        // default to returning the value unaltered
        return v;
    }
};

function CaveMan(name,discovered) {
    this.name       = name;
    this.discovered = discovered;
};
CaveMan.prototype.getName = function () {
    return this.name + ", the cave man";
}

// Static methods to convert to and from a basic object structure
CaveMan.thaw = function (o) {
    return new CaveMan(o.n, o.d);
};
// Convert to a basic object structure including a class identifier
CaveMan.freeze = function (cm) {
    return {
        _class : 'CaveMan',
        n : cm.name,
        d : cm.discovered // remains a Date for standard JSON serialization
    };
};

Demo.data    = {
    count : 1,
    type  : 'Hominid',
    specimen : [
        new CaveMan('Ed',new Date(1946,6,6))
    ]
};

Event.on('demo_freeze','click',function (e) {
    Demo.jsonString = JSON.stringify(Demo.data, Demo.cryo);

    Dom.get('demo_frozen').value = Demo.jsonString;
    Dom.get('demo_thaw').disabled = false;
});

Event.on('demo_thaw','click',function (e) {
    var parsedData = JSON.parse(Demo.jsonString, Demo.revive);
        cm = parsedData.specimen[0];

    Dom.get('demo_thawed').innerHTML =
        "<p>Specimen count: " + parsedData.count + "</p>"+
        "<p>Specimen type: " + parsedData.type + "</p>"+
        "<p>Instanceof CaveMan: " + (cm instanceof CaveMan) + "</p>"+
        "<p>Name: " + cm.getName() + "</p>"+
        "<p>Discovered: " + cm.discovered + "</p>";
});

});
</textarea>

<h2>Configuration for This Example</h2>

<p>You can load the necessary JavaScript and CSS for this example from Yahoo's servers.  <a href="http://developer.yahoo.com/yui/articles/hosting/?dom&event&json&MIN#configure">Click here to load the YUI Dependency Configurator with all of this example's dependencies preconfigured</a>.</p>

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							<p class="loggerButton"><span id="loggerLink"><span class="first-child"><a href="json_freeze_thaw_log.html">Reload with logging<br />
	 and debugging enabled.</a></span></span></p></div>
	
						</div>
					
				
					<div id="examples">
						<h3>JSON Utility Examples:</h3>
	
						<div id="exampleToc">
							<ul>
								<li><a href='../json/json_connect.html'>JSON with Connection Manager</a></li><li class='selected'><a href='../json/json_freeze_thaw.html'>Rebuilding class instances from JSON data</a></li><li><a href='../json/json_convert_values.html'>Adding new object members during parsing</a></li>							</ul>
						</div>
					</div>
					
					<div id="module">
						<h3>More JSON Utility Resources:</h3>
						<ul>
							<li><a href="http://developer.yahoo.com/yui/json/">User's Guide</a> (external)</li>
						<li><a href="../../docs/module_json.html">API Documentation</a></li>
                            
                            
							<li><a href="http://yuiblog.com/assets/pdf/cheatsheets/json.pdf">Cheat Sheet PDF</a> (external)</li></ul>
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